1. Field of the Invention
The present invention relates to a method of micro-processing to be applied in the production of semiconductor integrated circuits utilizing a radiation sensitive negative resist, particularly to a method of forming patterns by the process of development.
2. Description of Prior Art
Conventionally, in the etching process for producing semiconductor integrated circuits, the most widely adopted practice has been the method of forming patterns by use of photo-sensitive resins (photo-resists) which are sensitive to visible and ultraviolet rays. In recent years, in order to meet with increasing demands for the higher integration of elements intended to improve the reliability and performance of circuits, intensive efforts have been made to establish the ultramicro-technique for forming circuit patterns. Among them, methods of forming high precision circuit patterns have been developed utilizing high energy radiations such as far ultraviolet ray, X-ray and electron beams in substitution for the conventional light beam. In the production of integrated circuits, a resist is applied on a base plate to form a thin film, on which a micro-pattern is printed by exposure to radiation followed by development. Then etching, especially dry etching by means of plasma, is applied to process the part of the base plate where the pattern has not been formed. However, recent demands are such that circuit patterns as small as 1 micron, and further submicron patterns must be proceeded. To meet with these demands, a high resolution radiation resist with good dry etching resistance must be developed and, in addition, a method of processing the resist, particularly a method of developing the micro-patterns must be established. From the point of dry etching resistance more attention has been given to radiation sensitive resists, particularly negative resists, which are prepared from a polymer of aromatic vinyl compound as raw material.
When the radiation sensitive resist is exposed to radiation, the irradiated portion turns into gel and becomes insoluble in a solvent due to the crosslinking reaction between polymer chains. Thus, in the developing process, a pattern can be formed by dissolving the non-irradiated portions in the liquid developer. However, when a micropattern is formed using the negative resist, swelling of the irradiated portion, if any during the developing, causes lowering of the resolution. Therefore, it is especially important to select an appropriate solvent system for the developer, so as to minimize the swelling of the irradiated portions as well as to accelerate dissolution of the non-irradiated portions. Further, consisting of development and surface conditions of the resist after the developing should be considered in the selection of optimum developers from the aspect working process.
The present inventors have made extensive studies and investigations on the development process of negative resists made from aromatic vinyl polymers with the mentioned requirements in mind, and finally arrived at the completion of this invention.